Recovering hydrocarbons from subterranean zones typically involves drilling wellbores.
Wellbores are made using surface-located drilling equipment which drives a drill string that eventually extends from the surface equipment to the formation or subterranean zone of interest. The drill string can extend thousands of feet or meters below the surface. The terminal end of the drill string includes a drill bit for drilling (or extending) the wellbore. Drilling fluid, usually in the form of a drilling “mud”, is typically pumped through the drill string. The drilling fluid cools and lubricates the drill bit and also carries cuttings back to the surface. Drilling fluid may also be used to help control bottom hole pressure to inhibit hydrocarbon influx from the formation into the wellbore and potential blow out at surface.
In some circumstances it is desirable to cause a drill bore to follow a trajectory that may include changes in direction. For example, it may be desirable to drill straight down to a desired depth and then cause the drill bore to turn so that the drill bore extends horizontally in a desired direction. Various directional drilling technologies have been developed to allow a rotary drill to be steered so as to cause a wellbore to follow a desired path. Rotary steerable technologies fall into two broad categories which can be described as “push-the-bit” and “point-the-bit”. Push-the-bit systems steer a drill bit by applying a side load that forces the bit laterally in a desired direction. The most common push-the-bit tools use pads on the outside of the tool which press against the well bore thereby causing the bit to drill more toward the opposite side causing a direction change. Point-the-bit systems steer the bit by tilting the bit in the direction of the desired curve. Point-the-bit systems generally include a bent section in the drillstring near the bit and a mud motor to drive the bit so that drilling can proceed without rotating the entire drill string. The bend points the bit in a direction different from the axis of the wellbore. By pumping mud through the mud motor, the bit turns while the drillstring does not rotate, allowing the bit to drill in the direction it points. When a desired wellbore direction is achieved, that direction may be maintained by rotating the entire drillstring (including the bent section) so that the bit does not drill in a single direction off the wellbore axis, but instead sweeps around and its net direction coincides with the existing wellbore.
RSS (Rotary steerable system) is another directional drilling technology. RSS tools allow steering while the drill string is rotating. Some RSS tools provide pads that can rotate relative to the drill string and are operable to steer the bit.
Bottom hole assembly (BHA) is the name given to the equipment at the terminal end of a drill string. In addition to a drill bit, a BHA may comprise elements such as: apparatus for steering the direction of the drilling (e.g. a steerable downhole mud motor or rotary steerable system); sensors for measuring properties of the surrounding geological formations (e.g. sensors for use in well logging); sensors for measuring downhole conditions as drilling progresses; one or more systems for telemetry of data to the surface; stabilizers; heavy weight drill collars; pulsers; and the like. The BHA is typically advanced into the wellbore by a string of metallic tubulars (drill pipe).
Electronics in a BHA may provide any of a wide range of functions including, without limitation: data acquisition; measuring properties of the surrounding geological formations (e.g. well logging); measuring downhole conditions as drilling progresses; controlling downhole equipment; monitoring status of downhole equipment; directional drilling applications; measuring while drilling (MWD) applications; logging while drilling (LWD) applications; measuring properties of downhole fluids; and the like. A BHA may include various sensors (e.g. sensors for use in well logging) that may include one or more of vibration sensors, magnetometers, inclinometers, accelerometers, nuclear particle detectors, electromagnetic detectors, acoustic detectors, and others; acquiring images; measuring fluid flow; determining directions; emitting signals, particles or fields for detection by other devices; interfacing to other downhole equipment; sampling downhole fluids; etc.
Downhole sensors may detect the direction and angle of inclination of the drill string near the drill bit. Data from such sensors may be used in directional drilling applications to help guide the borehole to follow a desired trajectory.
A downhole probe may communicate a wide range of information to the surface by telemetry. Telemetry information can be invaluable for efficient drilling operations. For example, telemetry information may be used by a drill rig crew to make decisions about controlling and steering the drill bit to optimize the drilling speed and trajectory based on numerous factors, including legal boundaries, locations of existing wells, formation properties, hydrocarbon size and location, etc. A crew may make intentional deviations from the planned path as necessary based on information gathered from downhole sensors and transmitted to the surface by telemetry during the drilling process. The ability to obtain and transmit reliable data from downhole locations allows for relatively more economical and more efficient drilling operations.
One or more systems may be provided for telemetry of data to the surface. Data telemetry techniques include transmitting information by generating vibrations in fluid in the bore hole (e.g. acoustic telemetry or mud pulse (MP) telemetry) and transmitting information by way of electromagnetic signals that propagate at least in part through the earth (EM telemetry). Other telemetry techniques use hardwired drill pipe, fibre optic cable, or drill collar acoustic telemetry to carry data to the surface.
Some patent references in the general field of the invention include: U.S. Pat. Nos. 5,738,178; 5,617,926; 6,092,610; 6,129,160; 7,549,467; 7,987,927; 8,322,461; GB2456421; CA2395082; CA2642713; and CA2647032.
There remains a need for alternative methods for directional drilling.